Glossary
Send As
An Exchange permission letting a delegated user send email as if they were the mailbox owner.
Send As is an Exchange Online permission that lets a delegated user send email as if they were the mailbox owner — recipients see the message as from the original mailbox, with no indication of the delegate. Different from Send on Behalf, which adds "on behalf of" to the From header so recipients see who actually sent. Send As is the right permission for shared mailboxes where all team members reply as the shared identity (support@company.com), for executive assistants sending email as the executive, or for service accounts sending automated mail as a no-reply address. Configured in Exchange Admin Center → Recipients → Mailbox → Manage mailbox delegation or via Add-MailboxPermission -AccessRights "SendAs" PowerShell.